Definition of legionella in US English:



  • 1The bacterium which causes legionnaires' disease, flourishing in air conditioning and central heating systems.

    Legionella pneumophila, a motile aerobic rod-shaped (or filamentous) Gram-negative bacterium

    ‘legionella could survive over a year inside pipes’
    count noun ‘some legionellae are sensitive to this drug’
    • ‘The legionella was discovered in the showers, water basins and toilets during a routine inspection.’
    • ‘The disease kills one in 10 of those who contract it and is caused by legionella bacteria.’
    • ‘Infection occurs when a person breathes in water droplets that are contaminated by many legionella bacteria.’
    • ‘Infection occurs from exposure to legionellae organisms in the environment.’
    • ‘There is no vaccine that can protect against legionella bacteria.’
    1. 1.1informal Legionnaires' disease.
      ‘whirlpool baths can trap water in the pump, risking legionella’
      • ‘When antibiotics active against atypical pathogens were used, only pneumonia related to legionella showed a statistically significant improvement in outcome.’
      • ‘She stressed that the Health Board was satisfied, based on expert clinical advice and national protocols for managing legionella, that ‘there was and is no immediate danger to other patients, staff or visitors in the hospital’.’


1970s: modern Latin, from legion + the diminutive suffix -ella.